Abstract
An individual's investment in mating or keeping a pair bond intact may be influenced not only by the attractiveness of its current mate, but also by that of other potential mates. In this study, we investigated the effect of relative attractiveness on pair-bond behaviour in bearded reedlings, Panurus biarmicus. We showed that mate attractiveness, in terms of beard length in males and tail length in females, influenced courtship behaviour when the pair was kept isolated. In the presence of a conspecific, contact initiations within a pair increased. This increment was mainly related to the sex of the unpaired conspecific, however, and less to differences in attractiveness between the current partner and the unpaired conspecific. Female contact initiations towards potential extra mates were independent of male attractiveness, whereas male contact behaviour was significantly influenced by female attractiveness. However, females displayed more contact initiations to their current mate when they were less attractive than the unpaired females. Males decreased their overtures towards other females with increasing attractiveness of their current mates. Overall, our results suggested that, when there was a risk of losing their mate, bearded reedlings adjust their pair-bond investment mainly in response to the presence or absence of a competitor, and fine-tune investment to a lesser extent in response to the attractiveness of that potential competitor.
Highlights
Animal decisions and their actions often occur in public [1,2,3,4,5,6]
Whenever mate choice is constraint, post-mating sexual selection may significantly influence the social relationship between pair mates, in birds, where only a small fraction of socially monogamous species show monogamy on the genetic level, and the intensity of sexual conflict can be intense [15,16,17,18]
We found no correlation between female relative attractiveness and male courtship behaviour in the presence of an unpaired female, nor between male relative attractiveness and female or male courtship behaviour in the presence of an unpaired male
Summary
Animal decisions and their actions often occur in public [1,2,3,4,5,6]. As a result, individuals can use social information to make decisions, and they may adjust their behaviour whenever conspecifics are present [7,8,9,10,11]. Petrie & Hunter [31] and Petrie & Kempenaers [25] predicted that, in socially monogamous species, the relative quality of the members of a pair is an important determinant for who invests more in maintaining the pair bond, especially when another option appears (i.e. a potential extra-pair or social mate). The degree of conflict depends on the attractiveness of the two pair members and another potential social or copulation partner [30,32] This degree of conflict may determine the individual behaviour towards other available individuals (e.g. investment in extra-pair behaviour, defence behaviour) or towards the current partner (e.g. mate guarding or other behaviours to maintain the pair bond) [32,33,34,35]. A cost of this sexual conflict related to individual variation in attractiveness is either the lost of paternity or the lost of the mate
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